AKT is a serine-threonine kinase identified as an oncogene in a mouse leukemia virus, and it has been revealed that its activity is important for various functions, such as cell proliferation, survival, metabolism, metastasis, and invasion (Non-patent Literature 1 and 2). In human beings, three isoforms (AKT1/PKBα, AKT2/PKBβ, and AKT3/PKBγ) have been reported (Non-patent Literature 3 and 4). Activation of AKT involves localization to the plasma membrane by binding to PI3 kinase-generated phosphatidylinositol 3-phosphate, and phosphorylation by multiple kinases (Non-patent Literature 5). In many cancers (e.g., breast cancer, pancreatic cancer, liver cancer, prostatic cancer, stomach cancer, lung cancer, ovarian cancer, head and neck cancer, urinary tract cancer, and endometrial cancer), it has been reported that the expression of activated AKT is enhanced by activation of PI3 kinase due to mutation, etc., or inactivation of its negative regulator, PTEN (Non-patent Literature 6). In addition, enhanced expression of activated AKT has been reported to be associated with poor prognosis in various cancers (e.g., breast cancer, pancreatic cancer, liver cancer, prostatic cancer, stomach cancer, and endometrial cancer) (Non-patent Literature 7).
Therefore, in cancers with enhanced activity of AKT, a drug that specifically inhibits AKT is expected to enable suppression of cancer cell proliferation, survival, metastasis, invasion, etc., by administration of the drug, and is anticipated as a new cancer treatment that will contribute to improvements in patient life-prolongation and QOL. In actual therapy, since PI3 kinase abnormality, PTEN abnormality, or AKT activation serves as an index for stratification, patient selection based on the stratification becomes possible; thus, this is highly favorable from an ethical viewpoint.